In a communication system assuming that a mobile station such as a train and an automobile traveling on a predetermined route performs radio communication with a base station, as described in Non Patent Literature 1, it is preferable that a base station equipped with directional antennas distributedly arranged along a traveling route of a mobile station be installed and the base station form an antenna beam along the traveling route. This makes it possible to configure an elongated cell along the traveling route, and to increase cell length while suppressing interference to other systems. A certain communication area, which is formed by transmission and reception of identical signals to and from a plurality of distributedly arranged antennas in synchronization at identical frequencies, is called a linear cell.
For example, the linear cell can be achieved in a form in which one communication modem is connected by an optical fiber or the like to a plurality of distributedly arranged antennas, or a form in which communication modems installed in antennas are synchronized with each other to have a common radio signal.
In a conventional multi-cell system including a plurality of cells, it is necessary to employ a frequency reuse factor of at least three in order to suppress inter-cell interference. On the other hand, by adopting a linear cell configuration, cell length can be increased and interference due to overreach is reduced, so that it is possible to construct a system employing a frequency reuse factor of two as indicated in Non Patent Literature 1, and frequency utilization efficiency is improved. Overreach is a phenomenon in which a signal transmitted from an antenna of a base station in a certain cell reaches a next adjacent cell beyond an adjacent cell.